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United States Patent |
5,168,241
|
Hirota
,   et al.
|
December 1, 1992
|
Acceleration device for charged particles
Abstract
An acceleration device for charged particles has an acceleration cavity
through which passes a beam of the particles. High frequency power from a
suitable source is transmitted to the cavity via a suitable transmission
means (antenna) to transmit the energy to the particles and so accelerate
them. The transmission means is controlled by a suitable control to
control the coupling constant of the transmission means when power is
applied. Also, the device may have a looped conductor in the cavity
controlled by the control to couple to the field in the cavity and to
extract power from the field, thereby to control the de-tuning of the
applied power relative to the power transmitted to the particles. By
controlling the coupling constant and/or the de-tuning, power may be
transmitted efficiently to the beam of particles.
Inventors:
|
Hirota; Junichi (Hitachi, JP);
Nishi; Masatsugu (Katsuta, JP)
|
Assignee:
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Hitachi, Ltd. (Tokyo, JP)
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Appl. No.:
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495617 |
Filed:
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March 19, 1990 |
Foreign Application Priority Data
Current U.S. Class: |
315/500; 333/231; 333/235 |
Intern'l Class: |
H05H 013/04 |
Field of Search: |
328/233,235
315/5.41,5.42
333/230,231,235
|
References Cited
U.S. Patent Documents
3043986 | Jul., 1962 | Podliusky | 328/233.
|
4794340 | Dec., 1988 | Ogasawara | 328/235.
|
4992745 | Feb., 1991 | Hirota et al. | 328/233.
|
Other References
Fukushima et al; Characteristics of RF Accelerating Cavity, Feb. 18, 1975,
Institute for Nuclear Study; pp. 1-25.
Evans et al; The 1 MV 114 MH.sub.Z Electron Accelerating System For the
CERN PS; Sep. 1987; pp. 1901-1903 IEEE.
|
Primary Examiner: Yusko; Donald J.
Assistant Examiner: Horabik; Michael
Attorney, Agent or Firm: Antonelli, Terry Stout & Kraus
Claims
What is claimed is:
1. An acceleration device for charged particles comprising:
an acceleration cavity;
a source activatable to generate high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate cavity power for controlling the
energy of said charged particles utilizing a magnetic coupling constant
between said high frequency power and said cavity power; and
control means for controlling said transmitting means so as to control said
magnetic coupling constant, said control means being arranged to act
during existance of said charged particles in said cavity.
2. A device according to claim 1, wherein said transmitting means is
coupled to said cavity in dependence on an area of said transmitting means
and a field strength, and said control means is arranged to vary said
field strength thereby to vary said coupling of said transmitting means to
said cavity.
3. A device according to claim 1, wherein said transmitting means is
coupled to said cavity, and said control means includes bias means for
applying a bias to said coupling of said transmitting means to said cavity
in dependence on a bias current, and current control means for controlling
said bias current so as to control said coupling of said transmitting
means to said cavity.
4. A device according to claim 3, wherein said bias means comprises at
least one magnetic body and at least one coil for causing said at least
one magnetic body to generate a bias magnetic field arranged to act on
said transmitting means.
5. An acceleration device according to claim 3, wherein said bias means is
connected to said cavity, and said current control means is arranged to
control said bias means so as to control detuning of said cavity power
relative to said high frequency power.
6. An acceleration device according to claim 1, further comprising detuning
control means for controlling detuning of an acceleration power relative
to said high frequency power.
7. An acceleration device according to claim 6, wherein said acceleration
power causes a field in said cavity; and said detuning control means
includes at least one looped conductor in said cavity for coupling with
said field and extracting power from said field, and means for controlling
the extraction of power from said field by said at least one looped
conductor.
8. An acceleration device according to claim 7, wherein said at least one
looped conductor is hollow.
9. An acceleration device according to claim 7, further including means for
detecting said detuning of said acceleration power relative to said high
frequency power, and for generating an output to said detuning control
means.
10. An acceleration device according to claim 7, wherein said means for
controlling the extraction of power from said field comprises a magnetic
body for influencing said coupling of said at least one looped conductor
with said field; and
means for controlling the specific magnetic permeability of said magnetic
body on said at least one looped conductor.
11. A device according to claim 1, wherein said transmitting means includes
an antenna for enabling generation of a magnetic field for coupling to
said cavity.
12. An acceleration device for charged particles comprising:
an acceleration cavity;
a source activatable to generate high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate cavity power for controlling the
energy of said charged particles, there being a coupling constant between
said high frequency power and said cavity power; and
control means for controlling said transmitting means so as to control said
coupling constant, said control means being arranged to act during
existence of said charged particles in said cavity;
wherein said transmitting means is also capable of generating reflected
power, and said control means is arranged to control said coupling
constant so as to control said reflected power.
13. A device according to claim 12 wherein said control means is arranged
to control said coupling constant such that said reflected power is
substantially zero.
14. An acceleration device for charged particles comprising:
an acceleration cavity;
a source activatable to generate high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate cavity power for controlling
energy of said charged particles, said transmitting means being coupled to
said cavity in dependence on an area of said transmitting means and a
field strength; there being a magnetic coupling constant between said high
frequency power and said cavity power; and
control means for controlling said transmitting means so as to control said
magnetic coupling constant, said control means being arranged to vary
field strength, thereby to vary said coupling of said transmitting means
to said cavity.
15. An acceleration device for charged particles; comprising:
an acceleration cavity;
a source activatable to generate high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate cavity power for controlling the
energy of said charged particles, said transmitting means also being
capable of generating reflected power; and
control means for controlling said transmitting means so as to control said
reflected power, said control means being arranged to act during the
existance of said charged particles in said cavity.
16. An acceleration device for charged particles, comprising:
an acceleration cavity;
a source for generating high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity said transmitting means being magnetically coupled
to said cavity in dependence on an area of said transmitting means and a
field strength/permeability relation of the coupling; and
means for varying said field strength/permeability relation so as to vary
the magnetic coupling of said transmitting means to said cavity.
17. An acceleration device for charged particles, comprising:
an acceleration cavity;
a source for generating high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity, said transmitting means being magnetically coupled
to said cavity;
bias means for applying a bias to said magnetic coupling of said
transmitting means to said cavity in dependence on a bias current; and
current control means for controlling said bias current so as to control
said magnetic coupling of said transmitting means to said cavity.
18. An acceleration device for charged particles, comprising:
an acceleration cavity;
a source for generating high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate cavity power in said cavity for
controlling the energy of said charged particles;
bias means for applying a bias to said cavity in dependence on a bias
current; and
current control means for controlling said bias current so as to control
detuning between the oscillation frequency of said high frequency power
source and the resonance frequency of said cavity power.
19. A device according to claim 18, wherein said bias means comprises at
least one magnetic body and at least one coil for causing said at least
one magnetic body to generate a bias magnetic field arranged to act on
said transmitting means.
20. A power coupler for an acceleration device for charged particles,
comprising:
transmitting means for transmitting high frequency power;
bias means for controlling said transmitting means, said bias means having
means for generating a bias magnetic field, said bias magnetic field being
arranged to act on said transmitting means so as to influence the
transmission of said high frequency power from said transmitting means;
and
a bias control means for controlling said bias means so as to control said
bias magnetic field and thereby control said transmission of said high
frequency power.
21. A power coupler according to claim 20, wherein said bias means
comprises at least one magnetic body and at least one coil for causing
said at least one magnetic body to generate a bias magnetic field arranged
to act on said transmitting means.
22. An acceleration device for charged particles, comprising:
an acceleration cavity;
means for applying high frequency power to said cavity so as to generate
cavity power in said cavity for controlling the energy of said charged
particles, said cavity power causing a field in said cavity; and
control means for controlling detuning of the oscillation frequency of said
high frequency power source and for controlling the resonance frequency of
said cavity power;
wherein said control means includes at least one looped conductor in said
cavity for coupling with said field in said cavity and extracting power
from said field, and means for controlling the extraction of power from
said field by said at least one looped conductor.
23. An acceleration device according to claim 22, wherein said at least one
looped conductor is hollow.
24. An acceleration device according to claim 22, further including means
for detecting said detuning of said acceleration power relative to said
high frequency power, and generating an output to said detuning
controller.
25. An acceleration device according to claim 22, wherein said means for
controlling the extraction of power from said field comprises a magnetic
body for influencing said coupling of said at least one looped conductor
with said field; and
means for controlling the specific magnetic permeability of said magnetic
body thereby to change the influence of said magnetic body on said at
least one looped conductor.
26. A detuning controller for controlling density of an acceleration device
for charged particles, comprising:
at least one looped conductor for coupling with a field so as to extract
power from said field;
a magnetic body for influencing said coupling of said at least one looped
conductor with said field; and
means for controlling the specific magnetic permeability of said magnetic
body, thereby to change the influence of said magnetic body on said at
least one looped conductor.
27. A detuning controller according to claim 26, wherein said at least one
looped conductor is hollow.
28. A ring type accelerator system comprising a plurality of magnets
defining a looped path for a beam of charged particles, and at least one
acceleration device in said looped path for controlling energy of said
beam;
said acceleration device comprising:
an acceleration cavity;
a source activatable to generate high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate cavity power for controlling
energy of said charged particles, there being a magnetic coupling constant
between said high frequency power and said acceleration power; and
control means for controlling said transmitting means so as to control said
magnetic coupling constant, said control means being arranged to act
during a circulatory motion of said charged particles.
29. A ring type accelerator system comprising a plurality of magnets
defining a looped path for a beam of charged particles, and at least one
acceleration device in said looped path for accelerating said beam;
said acceleration device comprising:
an acceleration cavity;
a source activatable to generate high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate acceleration power for
accelerating said charged particles, said transmitting means also being
capable of generating reflected power; and
control means for controlling said transmitting means so as to control said
reflected power, said control means being arranged to act during
activation of said power source.
30. A ring type accelerator system comprising a plurality of magnets
defining a looped path for a beam of charged particles, and at least one
acceleration device in said looped path for controlling energy of said
beam; said acceleration device comprising:
an acceleration cavity;
a source for generating high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity, said transmitting means being magnetically coupled
to said cavity in dependence on an area of said transmitting means and a
field strength/permeability relation of the coupling; and
means for varying said field strength/permeability relation so as to vary
the magnetic coupling of said transmitting means to said cavity.
31. A ring type accelerator system comprising a plurality of magnets
defining a looped path for a beam of charged particles, and at least one
acceleration device in said looped path for controlling energy of said
beam; said acceleration device comprising:
an acceleration cavity;
a source for generating high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity, said transmitting means being magnetically coupled
to said cavity;
bias means for applying a bias to said magnetic coupling of said
transmitting means to said cavity in dependence on a bias current; and
current control means for controlling said bias current so as to control
said magnetic coupling of said transmitting means to said cavity.
32. A ring type accelerator system comprising a plurality of magnets
defining a looped path for a beam of charged particles, and at least one
acceleration device in said looped path for controlling said beam; said
acceleration device comprising:
an acceleration cavity;
a source for generating high frequency power;
transmitting means for transmitting said high frequency power from said
source to said cavity so as to generate cavity power in said cavity for
controlling said beam;
bias means for applying a bias to said cavity in dependence on a bias
current; and
current control means for controlling said bias current so as to control
detuning of the oscillation frequency of the high frequency power source
and the resonance frequency of said cavity.
33. A ring type accelerator system comprising a plurality of magnets
defining a looped path for a beam of charged particles, and at least one
acceleration device in said looped path for controlling said beam; said
acceleration device comprising:
an acceleration cavity;
means for applying high frequency power to said cavity so as to generate
cavity power in said cavity for controlling said charged particles, said
cavity power causing a field in said cavity; and
control means for controlling detuning of the oscillation frequency of high
frequency power source and the resonance frequency of said cavity;
wherein said control means includes at least one looped conductor in said
cavity for coupling with said field in said cavity and extracting power
from said field, and means for controlling the extraction of power from
said field by said at least one looped conductor.
34. A method of controlling synchrotron acceleration of a beam of charged
particles using an acceleration device; comprising:
applying high frequency power to said acceleration device so as to
accelerate said beam;
controlling the detuning of the high frequency power to the beam; and
controlling the coupling constant of the high frequency power to the beam;
wherein each of said control of detuning and said control of the coupling
constant are simultaneous with the application of said high frequency
power.
35. A method of controlling a ring-type accelerator system, comprising the
steps of:
injecting charged particles into said system to form a beam of said charged
particles;
repeating said injection step a plurality of times thereby to increase in a
plurality of steps the number of said charged particles in said beam; and
controlling the detuning defined frequency difference between said high
frequency power and accelerating power of said particles during the
injection step.
36. A method according to claim 35, wherein said step of controlling said
detuning is pre-programmed in advance of said step of injecting charged
particles.
37. A method according to claim 35, further comprising the step of
detecting said detuning between each said repetition of said injection
step, and said step of controlling detuning is carried out in dependence
on said detected detuning.
38. A method according to claim 35, wherein the ring-type accelerator
system includes a synchrotron ring.
39. A method according to claim 35, wherein the ring-type accelerator
system includes an accumulator ring.
40. A method of controlling synchrotron acceleration of a beam of charged
particles using an acceleration device comprising:
applying high frequency power to said acceleration device so as to
accelerate said beam;
controlling said high frequency power to the beam; and
controlling a magnetic coupling constant of said high frequency power to
the beam.
41. A method of controlling a ring-type accelerator system, comprising the
steps of:
injecting charged particles onto said system to form a beam of said charged
particles;
repeating said injection step a plurality of times thereby to increase in
plurality of steps the number of said charged particles in said beam; and
controlling said high frequency power to the beam during the injection.
42. A method according to claim 41, wherein the ring-type accelerator
system includes a synchrotron ring.
43. A method according to claim 41, wherein the ring-type accelerator
system includes an accumulator ring.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acceleration device for charged
particles. It also relates to an accelerator system incorporating such a
device.
2. Summary of the Prior Art
It is known to generate synchrotron radiation using a ring type accelerator
as the synchrotron radiation generator. In a synchrotron accelerator or in
a storage ring, a beam of charged particles is accelerated to a storage
energy. In order to do that, particles at low energy are obtained, and
injected into the ring for acceleration to high energy. When synchrotron
radiation is needed for industrial purposes, it becomes important that the
synchrotron radiation generator is relatively compact. Generally, an
industrial synchrotron radiation generator has a linear accelerator which
creates a beam of charged particles and accelerates it to a low energy
level, a synchrotron which raises the low energy charged particle beam to
a higher energy level, and an accumulation ring which accelerates the beam
even further and accumulates the beam of charged particles.
As stated above, it is desirable that an industrial synchrotron radiation
generator occupies a small area. This enables the generator to be
installed in e.g. a semiconductor fabrication factory. A high brightness
(i.e. large current) is also necessary to reduce the irradiation time. To
meet the requirement of a small area it is, of course, necessary to make
each unit element smaller. However, if by using only an accumulation ring,
a charged particle beam can be synchrotron accelerated from a low energy
level to a final energy level in a stable way, the synchrotron stage can
be omitted and the size of the system reduced significantly.
A charged particle beam is accelerated with energy supplied from a high
frequency power source through a high frequency (radio frequency)
acceleration cavity. To achieve stable synchrotron acceleration of a
charged particle beam with a high frequency acceleration cavity,
synchrotron phase stability (hereinafter referred simply to as phase
stability, which will be explained in more detail later) must be achieved.
When a charged particle passes through a high frequency acceleration
cavity, an electric field is created by this current, and with this
electric field, a voltage is generated in opposite phase to the
acceleration voltage which is generated from the high frequency power
source (hereinafter this voltage in opposite phase is referred to as the
voltage induced by the beam). As a result, the charged particles lose a
part of the energy supplied and it becomes difficult to ensure the
stability of the beam around the looped path. Thus, the charged particles
cannot maintain a satisfactory phase stability. Such an effect becomes
greater as the number of charged particles in the beam increases, i.e. as
the beam current increases. Hereinafter, the gap between the oscillation
frequency of the high frequency power source and the resonance frequency
of the high frequency acceleration cavity will be referred to as the
de-tune value, and the creation of such gap as detuning.
One method of synchrotron acceleration of charged particles is discussed in
the study "Characteristics of a high frequency acceleration cavity"
(INS-TH-96. Institute of Nuclear Study, Tokyo University, Feb. 18, 1975).
This conventional technology adopts the method of maintaining a constant
acceleration voltage to the charged particles by controlling the high
frequency power only, which is the source of the power supply to the high
frequency acceleration cavity.
A high frequency acceleration cavity is discussed in the IEEE Partial
Accelerator Conference (1987) pp. 1901 to 1903. To change the resonance
frequency, the high frequency acceleration cavity must be transmitted onto
the magnetic body which consists of a tuner. The aforementioned
conventional technology uses a method of capturing the high frequency
magnetic field in a cavity then transmitting it by using a coaxial
transmission line.
In the high frequency acceleration cavity discussed above, the capturing of
the high frequency magnetic field was via a coaxial cable, and this method
permitted only a small change in the detuning. In low current
applications, this is not a problem, but it becomes so at higher current
where the amount of detuning is greater.
SUMMARY OF THE INVENTION
The two known systems described above each have their own problems.
The problem of the first system is that it requires an unnecessarily high
capacity, high frequency power source. The electric power from the high
frequency power source is magnetically coupled and impressed in a high
frequency acceleration cavity with a high frequency antenna. The coupling
constant, which represents the degree of the coupling, depends on the
energy of the charged particle and on the current. However, since the
coupling constant is kept at a fixed value, if the energy varied over a
wide range or if the current fluctuated, the system cannot respond
properly. Therefore, the power from the high frequency power source cannot
be effectively impressed into the high frequency acceleration cavity. In
other words, a high frequency power source more than necessary is needed
in order to supply the necessary electric power to the high frequency
acceleration cavity in view of the application efficiency.
Also, the synchrotron acceleration at a large current is not always stable.
As previously described, when a large current flows into the high
frequency acceleration cavity, it reduces the energy supplied to the
charged particles by the beam-induced voltage. Stable synchrotron
acceleration will not be achieved simply by enhancing the capacity of the
high frequency power source to compensate this reduced energy.
In the second system, the energy is transmitted through a coaxial
transmission line, however, because of a great attenuation of the high
frequency magnetic field strength on the coaxial transmission line, the
detune value cannot be enhanced.
In order to overcome these problems, the present invention permits control
of either or both of the coupling constant and the detuning. The latter is
the relationship between the high frequency power input to the cavity and
the accelerating power generated for transmission to the charged
particles. The latter has already been discussed, and relates to the beam
induced current. In order to control the coupling constant, it is possible
to detect power which is reflected from the cavity. Such power represents
the power which is not converted to acceleration power, and thus by
controlling this, the coupling constant can be controlled. Prefereably,
that control as such has to ensure that the reflect power is substantially
zero. In order to transmit power to the cavity, the transmitting device
should be magnetically coupled to the cavity, and there is a
field/permeability relation controlling that coupling. The present
invention proposes that that field strength/permeability relation be
controlled to vary the magnetic coupling, and so vary the coupling
constant. In order to do this, a bias is applied to the magnetic coupling
of the transmitting means to the cavity, and a bias current to that
control means is controlled. That bias preferably is performed by a
magnetic body at a coil controlled by the bias current, so that a bias
magnetic field is generated which acts on the means for transmitting the
high frequency power to the cavity.
As mentioned above, the present invention may also include detuning
control. In this case, the detuning control includes at least one looped
conductor in the cavity which couples to the field in the cavity and
extracts power from the field. Suitable means is provided for controlling
that power extraction. It has been found that a looped conductor does not
attenuate the power transmitted thereby, so that the problems of the prior
art coaxial arrangement are no longer present, and control and detuning
over a wide range can be achieved.
Preferably, the extraction of power is controlled by a magnetic body which
effects the coupling of the looped conductor to the field, and a power
source connected to that magnetic body is controlled so as to change the
specific magnetic permeability of the body.
Suitable means may be provided for detecting the detuning of the
acceleration power relative to the high frequency power, and the control
in the detuning control means thereby. Alternatively, an automatic
arrangement may be used.
It has also been found that the coupling constant controller arrangement
discussed above, if connected to the cavity, will also at least partially
control the detuning.
Finally, it is important to know that the control means for controlling the
coupling constant and/or the detuning are arranged to operate during the
activation of the power source. It is important that control of the
coupling constant and detuning is achieved whilst the beam is being
stored, as otherwise high beam currents cannot be achieved.
The present invention has further aspects. For example, the above
acceleration device may be used in a ring type accelerator comprising a
plurality of bending matters defining a loop path for the beam, and
acceleration of the beam is then achieved thereby. Furthermore, the power
coupler and detuning controller themselves are independent aspects of the
present invention. Finally, the present invention relates to a method for
controlling synchrotron radiation. In one development, this involves
controlling of detuning and/or controlling of coupling constant
simultaneous with the application of the high frequency pattern.
Furthermore, the present invention permits the power/detune characteristic
to be controlled so as to eliminate a region in which the beam is
unstable, thereby allowing high beam currents to be achieved. Moreover,
the present invention permits the detuning to be controlled at successive
injections of charge particles into the beam, so that the beam can at all
times be maintained in a tuned state.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described in detail, by
way of example, with reference to the accompanying drawings, in which:
FIG. 1 shows schematically an accelerator in which an acceleration device
according to the present invention may be used;
FIG. 2 is a diagram for explaining the action of a radio frequency
acceleration cavity;
FIG. 3 is a diagram useful for explaining phase stability;
FIG. 4 is a diagram illustrating the relationship between acceleration
cavity voltage, acceleration voltage and radio frequency power source
voltage before and after a de-tune, and also showing beam induced voltage;
FIG. 5 is a sectional view through a first embodiment of an acceleration
device according to the present invention;
FIG. 6 is a sectional view of the embodiment of FIG. 5, viewed at right
angles to the view in FIG. 5;
FIG. 7 is a detailed view of a power coupler used in the first embodiment
of the present invention;
FIG. 8 is a detailed view of a tuner used in the first embodiment of the
present invention;
FIG. 9 shows alternative flapper couplings for use in the tuner of FIG. 8;
FIG. 10 shows a second embodiment of an acceleration device according to
the present invention;
FIG. 11 shows a third embodiment of an acceleration device according to the
present invention; and
FIG. 12 shows a fourth embodiment of an acceleration device according to
the present invention.
DETAILED DESCRIPTION
FIG. 1 shows a schematic view of a ring type acceleration device for
generating synchrotron radiation. As shown in FIG. 1, a beam of charged
particles such as electrons or ions is accelerated using a linear
accelerator 21. From the linear accelerator 21, the charged particles are
injected via injector 22 to form a beam 6 in the acceleration device. The
beam 6 is caused to move in a looped path by a pair of bending magnets 23
which each bend the beam through 180.degree.. The beam 6 is maintained in
a converged state by quadrupole electromagnets 24. The beam 6 injected by
the injector 21 is supplied with radio frequency energy from an
acceleration device 1 (to be discussed in detail later) so that the energy
of the beam 6 increases each loop of the beam path.
FIG. 1 shows that when the beam 6 is caused to change direction due to the
bending magnets 23, the beam emits light in the form of synchrotron
radiation 25. FIG. 1 also shows a detector 28 for detecting the parameters
of the beam (e.g. beam energy) and for controlling the acceleration device
1.
Next, the importance of the coupling constant of the radio frequency
acceleration cavity (acceleration device) will be explained with reference
to FIG. 2.
FIG. 2 shows the fundamental construction of the radio frequency
acceleration device 1 having an acceleration cavity 11. Generally, a radio
frequency acceleration cavity has a power coupler 3 which impresses
electric power, a tuner 5 which controls the de-tune value, and a beam
duct 12 through which the beam 6 passes. The charged particles 9 of the
beam 6 are accelerated by an acceleration voltage V.sub.a which is
generated in the vicinity of an acceleration gap 13 when the beam passes
through the beam hole 12. This acceleration voltage V.sub.a is formed by
the power applied to the interior of the cavity 11 via a radio frequency
antenna 31 of the power coupler 3 from a radio frequency power source 4.
Hence, the efficiency of the application of power to the interior of the
cavity 11 depends upon the magnetic coupling between the radio frequency
antenna 31 and the cavity 11. Therefore, if the coupling constant .beta.,
which indicates the efficiency of coupling, is controlled so as to
minimise the reflected power, i.e. the power which is not applied to the
interior of the cavity but is reflected by the power coupler 3, the
acceleration voltage is formed using the minimum radio frequency power. In
addition, in FIG. 2 there is shown the wall 18 of the cavity.
Thus, the coupling constant .beta. is a measure of the relationship between
the high frequency power applied from the source 4 to the antenna 31
(transmission means) and the high frequency power applied from the antenna
31 to the cavity 11.
Next, referring to FIG. 3, the meaning of phase stability will be
explained. FIG. 3 shows the change in the acceleration voltage V.sub.a
with time, the acceleration voltage V.sub.a being generated in the
accelerating part (see FIG. 2) of the beam duct 12. In FIG. 1, when the
energy of the individual charged particle of the beam which is injected
from the linear accelerator 21 rises above 1 MeV, the velocity of the
charged particles approaches the speed of light. After that, the velocity
of the charged particles remains the same even with further acceleration.
At an energy above 1 MeV, a charged particle is not accelerated in speed
but increases in energy. On the other hand, when the energy of the charged
particles is increased, the radius of the track of the particle increases
at the deflecting part where the bending magnets 23 are located.
Therefore, in order to force the beam to follow a circulatory motion on
the same track, the centripetal force applied by the bending magnet 23,
that is to say, the strength of the magnetic field of the bending magnet
23 must increase with the increase in beam energy. This way of forcing the
beam to take a fixed circulatory track by increasing the strength of the
magnetic field of the bending magnet with increasing beam energy is called
synchrotron acceleration. When charged particles with energy above 1 MeV
are synchrotron accelerated, provided each charged particle of the beam
has the same energy, each charged particle will go around the track in
almost the same time. However, in practice, there is some scattering of
the energy of the charged particles. As a result, a charged particle with
a higher energy level follows a wider track and takes more time to
complete a loop of the track, of the beam 6. Similarly a charged particle
with a lower energy level takes less time. Thus there is a scattering in
the time that the charged particles reach the accelerating part 121. In
FIG. 3, the time coordinates proceed from left hand to the right hand
side. Therefore consider a charged particle B having a higher energy than
that of a charged particle A which particle A is in synchronism with the
deflection magnetic field, in other words has average energy of a beam.
Then, the particle B arrives later than the particle A, and thus the
particle B is accelerated with an acceleration voltage V.sub.ah which is
lower than V.sub.a. Hence, the energy added to the charged particle B is
less than that added to the charged particle A. This tends to cause the
particle B to catch up with the particle A having the average energy. In
most cases, the energy becomes less than average when it catches up with
the charged particle A, so it goes round the circulatory track at a higher
velocity. Again, the higher velocity causes a higher acceleration voltage,
so the particle tends to go around more slowly. That is, many charged
particles go round the looped path with oscillating energy (referred to as
synchrotron oscillation) within a range of phase, shown in FIG. 3. The
phase, as used here in the term "phase stability", means the phase of the
acceleration voltage against a charged particle (hereinafter referred to
as the acceleration phase). " Phase stability" means that the nature of
the acceleration phase is such as to make stable the synchrotron
oscillation. The condition in this state is called the "phase stability
condition". For the charged particle to make a stable synchrotron
oscillation without deceleration, it is necessary for the particle to fall
within a region where positive energy is supplied to the charged particle
from an acceleration phase .phi., and the particle must make a stable
energy oscillation, that is to say, denoting the base point of
acceleration phase .phi. by time a, it is necessary that .phi. falls in
the region 0<.phi.<.pi./2.
FIG. 4 is a diagram illustrating the relationship between the acceleration
cavity voltage V.sub.c, the acceleration voltage V.sub.a, shown in FIG. 3,
the radio frequency power source voltage P.sub.g which forms V.sub.c and
the voltage V.sub.a induced by the beam V.sub.b. The acceleration voltage
V.sub.a can be determined using the acceleration cavity voltage V.sub.c,
and the acceleration phase .phi., from FIGS. 3 and 4.
V.sub.a =V.sub.c cos .phi. (1)
The acceleration cavity voltage V.sub.c which is generated in the cavity is
represented by the vector sum of the radio frequency power source voltage
V.sub.gd, which is generated after de-tune in the acceleration cavity
delayed by a de-tune angle (4) (de-tune value converted into a phase
change) in conformity with the de-tune change and the voltage induced by
the beam V.sub.bd. Both V.sub.gd and V.sub.bd fall on circles having
diameters OV.sub.gr, OV.sub.br which are formed by the radio frequency
power source voltage before the de-tune voltage V.sub.gr and the induced
voltage by beam V.sub.br, thus, V.sub.a in formula (1) can be expressed by
formula (2) using V.sub.gr and V.sub.br.
V.sub.a =V.sub.gr cos .psi. cos (.theta.+.psi.)=V.sub.br
.multidot.cos.sup.2 .psi. (2).
The acceleration voltage at the existence of the beam is expressed by
formula (2), in which, however, V.sub.br changes with the synchrotron
oscillation and, therefore, has practically no effect on the phase
stability. Accordingly, in formula (2), only component V.sub.gr determines
phase stability.
Note that the condition for phase stability: 0<.phi.<.pi./2 is equivalent
to: dV.sub.a /dt<0.
Since the phase angle .theta. between the radio frequency power source
voltage before de-tune and the acceleration voltage can be varied with a
phase shifter (not illustration),
dV.sub.a /dt<0 can also be expressed as:
##EQU1##
Substituting formula (2) into formula (3), to calculate dV.sub.a
/d.theta., converts the phase stability condition into:
V.sub.gr cos .psi. sin (.theta.+.psi.)>0 (3).
This is rearranged into formula (4) by eliminating .theta. from the
equation for the component of the acceleration cavity voltage V.sub.c
which is perpendicular to the acceleration voltage V.sub.a, giving:
##EQU2##
where, i.sub.o : Beam current
R.sub.sh : An equivalent resistance to create induced voltage V.sub.br
(R.sub.sh =V.sub.br /i.sub.o)
.beta.: Coupling constant
.psi.: De-tune angle (the quantity determined by de-tune value .DELTA.f)
V.sub.c : Acceleration cavity voltage
.phi.: Acceleration phase.
Accordingly, in the case of synchrotron acceleration, since the
acceleration voltage V.sub.c, and the acceleration phase .phi. are
quantities determined by the strength generated in the bending magnet 23,
it is possible to change the de-tune value .DELTA.f and the coupling
constant .beta., and to control both values to satisfy the formula (4). In
addition, the inequality (4) indicates that controlling the de-tune value
.DELTA.f only is insufficient to maintain phase stability.
An embodiment of the invention will now be described referring to FIGS. 1,
and 5 to 9. This embodiment of the invention is for an industrial light
generator which has means for changing the coupling constant and means for
changing the de-tune value over a wide range in a high frequency
acceleration cavity.
FIG. 1 shows the general construction of the light generator being an
accelerator to which the present invention is applied. As explained above,
the light generator consists of a linear accelerator 21 as a preliminary
accelerator, an injector 22, which injects a PG,18 beam from the linear
accelerator 21 so that the beam 6 follows a circulatory track, a high
frequency acceleration cavity 1, which supplies energy to the injected
beam, a bending magnet 23, which turns the beam track so that the beam can
make a circulatory motion, and a plurality of quadrupole magnets 24, which
converges the beam to avoid divergence in a radial direction. The beam
injected from the injector 22 is supplied with energy from the high
frequency acceleration cavity 1, then its energy increases with every loop
of the circulatory track. When the beam changes its direction due to the
bending magnets 24, it emits radiant light 25 in the tangential direction
of the circulatory track. The radiant light 25 is taken out and may be
used to etch a semiconductor.
FIG. 5 shows an embodiment of a high frequency acceleration cavity 1 to
which the present invention is applied. FIG. 5 shows a sectional view from
above. FIG. 6 is a sectional view of the high frequency acceleration
cavity 1 shown in FIG. 5 viewed in the direction of the beam. The high
frequency acceleration cavity 1 comprises a power coupler 3, a high
frequency power source 4, a tuner 5, a cavity 11 in which a high frequency
electro-magnetic field is formed, and a beam duct 12 through which the
beam 6 passes (the beam 6 comprising charged particles 9). Inside the
cavity 11, as shown in FIG. 6, a predetermined vacuum pressure is
maintained by a vacuum pump 8. The power coupler 3 applies high frequency
electric power by forming a high frequency magnetic field 14, which is
shown in FIGS. 5 and 6, in the cavity 11 by supply of high frequency
current to a high frequency antenna 31. In FIG. 5, the symbol means that
the magnetic flux is in a direction from the face to the back of the
sheet, and the symbol x means that the flux is in inverse direction from
the back to the face. The high frequency magnetic field 14 forms a high
frequency acceleration electric field 15 in the beam duct 12 and creates
the acceleration voltage V.sub.a. The beam 6 is accelerated by this
acceleration voltage V.sub.a and increases its energy. The tuner 5 changes
the form of the high frequency magnetism in the cavity 11 by changing the
condition of magnetic coupling with the high frequency magnetic field 14,
thus it changes the resonance frequency in the cavity, that is to say, the
de-tune value.
First, referring to FIGS. 5 and 7, the means of changing the coupling
constant will be explained, which change is a first object of the present
invention.
FIG. 7 shows a detailed diagram of the power coupler 3 which has means for
changing the coupler constant. The power coupler 3 consists of a coaxial
transmission tube 34, which is a main body case, the high frequency
antenna 31, which has loop construction and runs through the coaxial
transmission tube 34 and allows magnetic coupling with the inside cavity
11 at one end, a ceramic window 33 which draws a high frequency magnetic
field which is generated by the high frequency current flowing in the high
frequency antenna 31 into a bias unit of a power coupler 32, and a
directional coupler 35 which measures the reflected power. The bias unit
of the power coupler 32 changes the strength of the bias magnetic field
which is generated on a power-use magnetic body 322 by changing the
magnitude of the current flowing in a power coil 321, thus controlling the
strength of the high frequency magnetic field which is drawn in through
the ceramic window 33. As a result, it is possible to change the strength
of the high frequency magnetic field H at the antenna part where the high
frequency antenna 31 couples magnetically with the interior of the cavity
11. The coupling constant .beta. between the radio frequency acceleration
cavity 1 and the radio frequency power source 4 is expressed by the
following formula:
.beta. .varies. .mu..sub.o H.sup.2 S.sup.2 (5)
where,
.mu..sub.o : Magnetic permeability of vacuum
H: The strength of high frequency magnetic field at the part of antenna
S: Area of coupling at the part of antenna
The equation (5) shows that the coupling constant .beta. can be changed by
changing the strength of high frequency magnetic field H and area of
coupling S. However, it is impossible to change the area of coupling S
during the circulatory motion of the charged particles, but the coupling
constant .beta. can be changed by changing the magnitude of the current
flowing in the power coil 321. For example, if the reflected power is
measured by the directional coupler 35, and the coupling constant .beta.
is controlled so as to make the reflected power equal to zero, then all of
the power generated by the radio frequency power source 4 can be applied
to the radio frequency acceleration cavity. In addition, FIG. 7 shows an
amplifier 71 for the reflected power which is detected by the directional
coupler 35, and is a driver amplifier 72 which sends a current into the
power coil 321. The control described above is performed by the
controlling equipment 7 of these units.
As is evident from the above explanation, high frequency power can be
efficiently applied to the high frequency acceleration cavity by providing
means for making the coupling constant .beta. of the high frequency
acceleration cavity changeable.
Next, referring to FIGS. 5 and 8, the action of the high frequency
acceleration cavity which allows a high de-tune, a second object of the
present invention, will now be described.
FIG. 8 shows a detailed diagram of the tuner 5 shown in FIG. 1. The tuner 5
consists of a looped construction forming a "flapper coupling" 51 which
magnetically couples with the high frequency magnetic field 14 in the
inside of the cavity 11, a ceramic window 53 which draws the high
frequency magnetic field 55 into a tuner bias unit 52 with a high
frequency current flowing in a flapper coupling 51 and the tuner bias unit
52. The flapper coupling 51 is a hollow conductor and is fixed on a tuner
port bottom plate 59.
The action of the flapper coupling will now be explained.
When the flapper coupling 51 is exposed to a magnetic field, a high
frequency current proportional to the area of intersection with the high
frequency magnetic field in the acceleration cavity flows in the flapper
coupling 51. In the flapper coupling 51, this high frequency current
returns directly to the magnetic body of the tuner 5. Therefore, the high
frequency magnetic field in the acceleration cavity can be transmitted to
the magnetic body without attenuation. If transmission without attenuation
is achieved, the ease of flow of high frequency current is greatly
influenced by change in the magnetic permeability, etc. of the magnetic
body. In other words, the magnetic impedance of the tuner 5 viewed from
the high frequency acceleration cavity changes greatly. As a result, the
reactance component of the high frequency cavity changes greatly, thus the
resonance frequency changes in the high frequency acceleration cavity,
that is to say, the de-tune value can be made to fluctuate over a wide
range.
In FIG. 8 the tuner bias unit 52 has substantially the same construction as
the power coupler bias unit 32. The tuner bias unit 52 consists of a
tuner-use magnetic body 522 which has the nature of specific magnetic
permeability .mu.>1 in the high frequency region, a tuner coil 521 which
generates a bias magnetic field H.sub.B, which is generated on the
tuner-use magnetic body 522 and a tuner yoke 523. A change in magnitude of
the bias magnetic field H.sub.B, which is generated on the tuner-use
magnetic body 522 causes a change in the specific magnetic permeability of
the tuner-use magnetic body .mu..sub.rf. This causes a change in the ease
of passing through the tuner-use magnetic body 522 for the high frequency
magnetic field 55. It is thus apparent that a field strength/permeability
relation exists. The value of .mu..sub.rf at this moment is expressed by
the following formula using the bias magnetic field H.sub.B :
.mu..sub.rf =1+4.pi. M.sub.s /H.sub.B (6)
where, M.sub.s : Saturated magnetization of the tuner-use magnetic body
522.
For example, if the passage of the high frequency magnetic field 55 is
difficult, then the flow of high frequency current in the flapper coupling
51 also becomes difficult. The fact that the flow of the high frequency
current is difficult means that the magnetic coupling condition
deteriorates for the flapper coupling 51 and inside the cavity 11. In
other words, there is a decrease in the high frequency magnetic field
inside the cavity 11 which intersects with the flapper coupling 51. This
causes a change in the shape of the magnetic field inside the cavity 11.
The change in shape of the magnetic field inside the cavity 11 causes a
change in the inductance L inside the cavity 11. The resonance frequency f
inside the cavity is expressed by following formula:
##EQU3##
where, L: Inductance inside the cavity
C: Capacitance inside the cavity
Therefore, by changing the current flowing in the tuner coil 521, the
specific magnetic permeability .mu..sub.rf of the tuner-use magnetic body
522 changes, affecting the resonance frequency f inside the cavity. In
other words, the de-tune value .DELTA.f can be changed. This change in
current in the tuner coil 521 is controlled by the controlling equipment 7
via an amplifier 72a (FIG. 5).
The de-tune value .DELTA.f is expressed by following formula, where the
stored energy in the cavity is denoted by U, the specific magnetic
permeability of the tuner-use magnetic body is denoted by .mu..sub.rf, the
high frequency magnetic field on the tuner-use magnetic body is denoted by
H.sub.c, the resonance frequency is denoted by f, the magnetic
permeability of vacuum is denoted by .mu..sub.o :
##EQU4##
where, .DELTA.v: Volume of the tuner-use magnetic body.
The above explanation and the formula (8), show that it is important for a
high de-tune value .DELTA.f to be obtained, so that the high frequency
magnetic field 14 in the cavity is transmitted to the tuner-use magnetic
body 522 without attenuation. In conventional technology, the high
frequency magnetic field 14 is captured by a loop antenna and transmitted
through a co-axial construction. Therefore, the strength of the high
frequency magnetic field is attenuated exponentially. Hence a high de-tune
value .DELTA.f cannot be obtained. On the other hand, in the present
invention, the high frequency magnetic field 14 is captured by the flapper
coupling 51 in the cavity 11 and can be directly transmitted to the
tuner-use magnetic body 522. Therefore, the high frequency magnetic field
strength can be transmitted without attenuation. As the result, a de-tune
value at least twice as large as that in conventional technology can be
obtained. In addition, the formula (8) shows that this method offers a
fine tuning range .mu..sub.rf times as great as the de-tune value obtained
by a conventional mechanical tuner.
Moreover, if the flapper coupling 51 requires cooling, very simple cooling
construction is available by sending coolant 54 through the interior of
the hollow conductor which forms the flapper coupling 51.
Furthermore, since this tuner has no moving parts in an ultra high vacuum,
the reliability of the tuner is increased. In this first embodiment of the
invention, the use of a single flapper coupling was explained for the sake
of simplicity. However, as shown in FIG. 9, a multiplicity of flapper
couplings 51 may be used in an arrangement in which the flapper couplings
51 are parallel or have a different angle for each flapper coupling 51.
As described above, in the present invention, a de-tune value twice as
great can be obtained by using a flapper coupling to make a coupling of
the high frequency magnetic field in the cavity. In addition, a simple
cooling construction is available by forming the flapper coupling from a
hollow conductor.
Next, referring to FIGS. 1 and 5, the means to maintain always synchrotron
phase stability and the method of performing synchrotron acceleration with
a satisfactory phase stability will be explained, which are the third and
fourth objects of the invention.
Suppose that a beam of low energy and a large current is injected from the
injector 22 and is synchrotron accelerated to a high energy level in a
stable condition. In synchrotron acceleration, the magnetic flux B of the
deflection magnetic field is changed by the bending magnet 23 in response
to the energy of the beam. In practice, an operation plan for the magnetic
flux B(t) of the bending magnetic field is prepared and the de-tune value,
etc. are controlled synchronously with B(t). That is to say, given the
bending magnetic field B(t.sub.o) at certain time t.sub.o, then the
acceleration voltage V.sub.a (t.sub.o) is determined as required by
consideration of the lost radiant light energy E.sub.loss of the beam 6
during its circulatory motion in order to cause the beam 6 to follow the
appropriate looped path. As it is difficult to measure the acceleration
voltage V.sub.a (t), the acceleration cavity voltage V.sub.c (t) and the
acceleration phase .phi.(t), which create the acceleration voltage V.sub.a
(t) are measured. In FIG. 5, the acceleration cavity voltage V.sub.c (t)
is measured by measuring the loop antenna 16. The acceleration phase
.phi.(t) cannot be measured. However, even if it cannot be measured, by
determining the acceleration cavity voltage V.sub.c (t), the beam makes
circulatory motion by itself thereby satisfying the acceleration phase
.phi.(t). The behavior of the beam is explained by reference to FIG. 3.
Assume the required acceleration voltage for the beam is V.sub.a, and the
acceleration cavity voltage simultaneously set is V.sub.c. Then a charged
particle 9 which is accelerated with an acceleration cavity voltage of the
value at point A takes the central circulatory track. Another charged
particle which is accelerated with a lower acceleration voltage V.sub.ah,
in other words, a charged particle accelerated earlier with a lower
energy, takes a different circulatory track as explained above. Therefore,
when the particle arrives at the high frequency acceleration cavity 1, the
particle tends to catch up with the particle that had been accelerated at
point A. Ultimately, the charged particle has a synchrotron oscillation
around point A and the beam is, on average, accelerated in the
acceleration phase .phi.. Accordingly, by setting the acceleration cavity
voltage V.sub.c at V.sub.c (t) which is synchronized with the deflection
magnetic field B(t), the control variables of the high frequency
acceleration cavity may be controlled. Specifically, since the
acceleration cavity voltage V.sub.c (t) and the acceleration phase
.phi.(t) are known, by controlling the coupling constant .beta. and the
de-tune angle .psi., which are on the left hand side of the inequality (4)
in the way such that the phase stability condition of the inequality (4)
is satisfied, a constantly stable synchrotron acceleration can be
achieved. The high frequency power P.sub.g (t) which is supplied by the
high frequency power source 4 is determined by the formula (9):
##EQU5##
Therefore, by setting the conditions for synchrotron acceleration such that
the deflection magnetic field B(t) will be increased, the acceleration
cavity voltage V.sub.c (t) and the acceleration phase .phi.(t) are
determined according to deflection magnetic field B(t), and by
determination of V.sub.c (t) and .phi.(t), the de-tune angle .phi.(t)
(de-tune value .DELTA.f (t)) and the coupling constant .beta.(t) are
determined so as to satisfy the inequality (4). Then, using formula (9),
the high frequency power P.sub.g is determined. By controlling the radio
frequency power source 4, the power coupler 3 and the tuner 5, stable
synchrotron acceleration can be maintained. This function is performed by
the controlling equipment 7. Previously described methods change the
coupling constant of the power coupler 3 and the de-tune value .DELTA.f of
the tuner 5.
Using this method, the controlling coupling constant .beta. and the de-tune
angle .psi. is adopted to satisfy the inequality (4), but this will not
always give a minimum value for the controlled high frequency power which
is determined by formula (9). A method for solving this problem is
described below.
The minimum consumption of high frequency power for control is achieved
when all the power transmitted on the high frequency antenna 31 of the
power coupler 3 is applied to the interior of the cavity 11, and is
controlled to create the required acceleration voltage. Thus it is
necessary to apply all of the high frequency power transmitted to the high
frequency antenna 31 to the interior cavity means to eliminate all
reflected power which has already been described above. However, the
following means is employed to get the required acceleration cavity
voltage V.sub.c. If the coupling constant .beta. is determined, the
acceleration cavity voltage V.sub.c is determined depending on the de-tune
value .DELTA.f and the high frequency power P.sub.g. Accordingly, the
actual acceleration cavity voltage V.sub.cr is measured by a measuring
loop antenna 16. The signal from the measuring loop antenna 16 is fed via
an amplifier 71a (FIG. 5) to the controlling equipment 7. Then the de-tune
value .DELTA.f and the high frequency power P.sub.g are controlled so as
to achieve the required acceleration cavity voltage V.sub.cp. As the
result, both the de-tune value .DELTA.f and the high frequency power vary
to compensate each other. For example, if the high frequency power P.sub.g
increases, then the de-tune value .DELTA.f varies to compensate for it, or
if de-tune value .DELTA.f changes, then high frequency power P.sub.g will
change to compensate for it. That is to say, the control progresses with
mutual compensation. This means, from the viewpoint of the high frequency
power P.sub.g, that control is progressing to have a minimum value power
against the difference in the de-tune value .DELTA.f.
Explanation will now be given of how the method described above always
satisfies the phase stability condition. The fact that the high frequency
power P.sub.g is controlled to take a minimum value through coupling
constant .beta. and de-tune value (de-tune angle .psi. (psi)) means that
the coupling constant .beta. and the de-tune angle .psi. (psi) are
controlled so as to satisfy the relationship of formula (10):
.differential..sup.2 P.sub.g /.differential..psi..multidot..alpha..beta.=0
(10)
where, applying the relation: .differential.P.sub.g /.differential..psi.=0,
the following is obtained
##EQU6##
Applying formula (11) to the inequality (4) of the phase stability
condition and rearranging it, the phase stability condition can be
expressed as follows:
.beta.>P.sub.b /P.sub.c -1 (12)
where,
P.sub.b =i.sub.o V.sub.a : Beam power consumption
P.sub.c =V.sub.c.sup.2 /R.sub.sh : Power loss at cavity wall
Applying formula (11) into formula (9) to get .differential..sup.2 P.sub.g
/i.psi..multidot..differential..beta.=0, then expressing it with P.sub.b
and P.sub.c :
.beta.=P.sub.b /P.sub.c -1 (13)
is obtained. Since formula (13) always satisfies the inequality (12), if
the high frequency power is controlled to a minimum at the coupling
constant of .beta. and the de-tune value of .DELTA.f, then a stable
synchrotron acceleration can be maintained.
As described above, if the control progresses to make the coupling constant
.beta. and de-tune value .DELTA.f satisfy the inequality (4) of the phase
stability condition, or to minimize the high frequency power, then a
stable synchrotron acceleration is maintained.
Next, referring to FIG. 10, a second embodiment of a high frequency
acceleration cavity will be explained which allows a high de-tune value.
Looking at formula (8), the appropriate de-tune value .DELTA.f can be
achieved by changing the strength of the magnetic field H.sub.b on the
tuner-use magnetic body instead of the magnetic permeability .mu..sub.rf
of the tuner-use magnetic body 522. In the second embodiment of the
present invention, means for changing the angle of a flapper coupling 51
is provided and the strength of the high frequency magnetic field H.sub.b
on the tuner-use magnet body is changed. With a change in the angle of the
flapper coupling 51, the intersecting area with the high frequency
magnetic field 14 inside the cavity 11 changes. Then the strength H.sub.b
of the high frequency magnetic field 55, which is introduced on the
tuner-use magnetic body, can be changed. If the rotation angle
.theta..sub.f of the flapper coupling is considered to be zero when the
flapper coupling takes a position parallel to the surface of the paper,
then the strength H.sub.b of the high frequency magnetic field 55, which
is introduced on the tuner-use magnetic body, is expressed by the formula
14:
H.sub.b =H.sub.bo cos.sup.2 .theta..sub.f (14)
where, H.sub.bo : The strength of the high frequency magnetic field 55 at
.theta..sub.f =0.
Control of the angle of the flapper coupling is achieved by driving a motor
512 while monitoring the actual angle by the controlling equipment 7 using
an angle detector 511. In addition, FIG. 10 shows an amplifier 513 to
drive the motor 512.
As explained above, this second embodiment of the invention also permits
the production of a high frequency acceleration cavity which allows a high
de-tune value by using a flapper coupling and changing its angle.
FIG. 11 shows a third embodiment of the high frequency acceleration cavity
which allows a high de-tune value with the high frequency electric field
in the cavity.
Normally, a high frequency magnetic field is generated in a direction
perpendicular to the direction of the beam and a high frequency magnetic
field is generated in the same direction as the forward direction of the
beam. Therefore as shown in FIG. 11, a tuner 5 may be attached to the side
of the high frequency acceleration cavity. The configuration of the tuner
for this case is substantially the same as in FIG. 8. However, to improve
coupling of the flapper coupling 51 and the high frequency electric field,
the flapper coupling 51 is prepared with smaller loop area. As the result,
similar to FIG. 8, a high frequency current flows on the flapper coupling
51, and the high frequency magnetic field is transmitted without
attenuation on the tuner-use magnetic body 521. Therefore, a high de-tune
value of .DELTA.f is achieved.
As explained above, by coupling the flapper coupling with the high
frequency electric field in the cavity, the high frequency acceleration
cavity allows a high de-tune value.
Referring to FIG. 12, a fourth embodiment of the invention being an example
of a high frequency acceleration cavity which has combined power coupler
and tuner will be explained.
As already discussed with reference to the first three embodiments of the
invention, the de-tune value of the high frequency acceleration cavity and
the coupling constant of a high frequency antenna can be controlled by
changing the strength of the high frequency magnetic field at respective
positions of the cavity. Therefore the fundamental construction of this
embodiment, which controls the de-tune value and the coupling constant at
one location similar to the arrangement shown in FIG. 7. Its difference
lies in its method of controlling the bias magnetic field. The following
is an example of the controlling method of this embodiment. If the current
which is sent into a power coil to change the coupling contant by the
reflected power obtained from a directional coupler 35 is denoted by
I.beta., and the current which is sent into the power coil to change the
de-tune value .DELTA.f by the difference between desired acceleration
cavity voltage V.sub.cp and the actual acceleration cavity voltage
V.sub.cr detected by a measuring loop antenna 16 is denoted by
I.DELTA..sub.f, then the current I which is sent into the power coil to
control the bias magnetic field is determined by formula (15):
I=.gamma.I.beta.+.delta.I.DELTA..sub.f (15)
where, .gamma.,.delta.: Weighing constants, which take values:
0<.gamma.,.delta.>1
Accordingly, by selecting the values for weighing constants in order to
satisfy the phase stability condition of inequality (4), the coupling
constant .beta. and the de-tune value .DELTA.f can be controlled in a
harmonized way. This control is performed by the controlling equipment 7.
As explained above, this embodiment, by a provision of a tuner function in
a power coupler realizes a simple construction of a high frequency
acceleration cavity with a secured phase stability.
In the above embodiments of the invention, the acceleration system used a
ring type accelerator which has a synchrotron function. However, the
invention also applies to an accumulation ring which has an accumulating
function only. In an accumulation ring of this type, the beam is
accumulated with a certain fixed energy. If the magnitude of the current,
which is injected into the accumulation ring, changes, it will be de-tuned
in response to the magnitude of the current and if the magnitude of the
current changes greatly, it will be necessary to provide a high frequency
acceleration cavity which has a high de-tune value. Notwithstanding this,
the present invention is effective for any ring type accelerator to
achieve efficient injection into the cavity with a minimum of reflected
power.
In addition, only one piece of controlling equipment 7 in the above
explanation is referred to. However, it is also possible to provide
separate pieces of controlling equipment for the high frequency
acceleration cavity and for the high frequency power source.
The present invention controls acceleration of a beam of charged particles
using an acceleration device by applying high frequency power to the
acceleration device so as to accelerate the beam, controlling the detuning
of the high frequency power to the beam, and controlling the coupling
constant of the high frequency power to the beam with the control of
detuning and the control of the coupling constant being effected
simultaneously with the application of the high frequency power.
Additionally, for control of a ring-type accelerator system utilizing a
synchrotron ring or an accumulator ring, charged particles are injected
into the system to form a beam of the charged particles with the injection
of the charged particles into the system being repeated a plurality of
times so as to increase in a plurality of steps the number of the charged
particles in the beam, and controlling detuning of a defined frequency
difference between the high frequency power and accelerating power of the
particles during the injection controlled. According to the present
invention, the controlling of the detuning is pre-programmed in advance of
the injecting of the charged particles. Furthermore, the detuning is
detected between each repetition of the injection step and the controlling
of the detuning is carried out in dependence on the detected detuning.
The present invention also enables control of synchrotron acceleration of a
beam of charged particles using an acceleration device by applying high
frequency power to the acceleration device so as to accelerate the beam,
controlling the high frequency power to the beam and controlling a
magnetic coupling constant of the high frequency power to the beam.
Additionally, control of a ring-type accelerator system includes injecting
charged particles into the system to form a beam of the charged particles,
repeating the injection a plurality of times so as to increase in a
plurality of steps the number of the charged particles in the beam and
controlling the high frequency power to the beam during the injection.
The present invention may have a configuration as described above, hence it
may exhibit the effects described below.
By providing a way of changing the coupling constant of a high frequency
acceleration cavity, high frequency power can efficiently be applied to
the high frequency acceleration cavity.
Furthermore, by providing a flapper coupling which has a loop shape part
which generates a magnetic field on its magnetic body, in the tuner of the
high frequency acceleration cavity, it is possible to have a high
frequency acceleration cavity, which permits a high de-tune value.
Furthermore, by providing a coil which changes the bias magnetic field of
the magnetic body, in the tuner of the high frequency acceleration cavity,
and changing the current, a high frequency acceleration cavity can be
produced which permits a high de-tune value of high reliability.
Alternatively by providing a flapper coupling and a means to rotate the
flapper coupling against a tune-use magnetic body, by changing the
rotation angle, it is also possible to provide a high frequency
acceleration cavity, which permits a high de-tune value. By measuring the
acceleration cavity voltage and the reflected power of the high frequency
power, by proper arrangement of their ratio contributing to the coupling
constant and the de-tune value, a high frequency acceleration cavity of a
simple construction which has a power coupler with a combined tuner is
possible.
Furthermore, by providing a power coupler which has means for changing the
coupling constant and a tuner which can change greatly the de-tune value,
it is possible to produce a ring type accelerator having synchrotron
function which can satisfy phase stability even for a large current.
Furthermore, by performing cooperative control which guarantees synchrotron
phase stability conditions for the coupling constant and de-tune value of
the high frequency acceleration cavity, stable synchrotron acceleration is
always possible.
Finally, by controlling the coupling constant and de-tune value of the high
frequency acceleration cavity to minimize the high frequency power, it is
possible to maintain stable synchrotron acceleration.
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